You'll notice that there is currently no real-time data available or King County Metro buses in OneBusAway. The issue is that King County Metro pulled the real-time feed because of the snow and adverse weather reroutes today. Why would they pull the real-time feed in conditions where you'd probably agree that it would be extra useful? They do so because the current tracking system for King County Metro buses doesn't work well when buses are on adverse weather reroute.
When a bus is on adverse weather reroute (see http://metro.kingcounty.gov/up/rr/adverseweather.html for a current list), real-time arrival predictions are not accurate for that route. Why is that?
The position of each bus in Metro KC is not tracked with GPS, but rather with a decidedly lower-tech approach. Each bus is outfitted with a device that can radio the current odometer reading for the bus back to a server. If we know the odometer reading when the bus starts its route, we can periodically monitor the real-time odometer readings to determine how far along the route the bus has traveled. This gives us an estimate of position and from there, an estimate of how early or late a bus is. This is how http://mybus.org works and OneBusAway is just a fancy front-end to MyBus.
The problem comes with buses on adverse weather reroute, or any type of temporary reroute. When a bus goes on reroute, the physical route changes and the odometry calculation based on the original route used above is no longer accurate. In a perfect world, we would know when a bus is on reroute and adjust to its new route. Unfortunately, there is currently no automated way for handling this situation.
The result, unfortunately, is that on days when it is often cold and miserable and you'd rather not wait outside any longer than you have to for your bus, the real-time tracker often doesn't work. Ironic, huh?
I'd argue that King County Metro went too far in cutting the ENTIRE feed, as there are plenty of buses that aren't on reroute where the real-time tracking would be extra useful to riders today. If you feel the same way, definitely let them know.